diff --git a/Bifrost.Security/Bifrost.Security.csproj b/Bifrost.Security/Bifrost.Security.csproj
index bbd3801..0a95d4f 100644
--- a/Bifrost.Security/Bifrost.Security.csproj
+++ b/Bifrost.Security/Bifrost.Security.csproj
@@ -1,9 +1,9 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net8.0</TargetFramework>
-    <ImplicitUsings>enable</ImplicitUsings>
-    <Nullable>enable</Nullable>
+    <TargetFramework>netstandard20</TargetFramework>
+    <ImplicitUsings>disable</ImplicitUsings>
+    <Nullable>disable</Nullable>
     <GeneratePackageOnBuild>True</GeneratePackageOnBuild>
     <PackageIcon>bifrost-icon.png</PackageIcon>
     <RepositoryUrl>https://github.com/Bifrost-Technologies/Bifrost.Security</RepositoryUrl>
diff --git a/Bifrost.Security/CryptoBytes.cs b/Bifrost.Security/CryptoBytes.cs
index f875c41..f556707 100644
--- a/Bifrost.Security/CryptoBytes.cs
+++ b/Bifrost.Security/CryptoBytes.cs
@@ -1,4 +1,5 @@
-using System.Runtime.CompilerServices;
+using System;
+using System.Runtime.CompilerServices;
 
 namespace Bifrost.Security
 {
@@ -126,7 +127,7 @@ internal static void InternalWipe<T>(ref T data)
         // * I didn't use a second loop variable to index into `c`, since measurement shows that calculating it from `i` is cheaper. 
         // * Using exactly `i < bytes.Length` as upper bound of the loop allows the JITter to eliminate bounds checks on `bytes[i]`, so I chose that variant.
         // * Making `b` an int avoids unnecessary conversions from and to byte.
-        public static string? ToHexStringUpper(byte[] data)
+        public static string ToHexStringUpper(byte[] data)
         {
             if (data == null)
                 return null;
@@ -144,7 +145,7 @@ internal static void InternalWipe<T>(ref T data)
 
         // Explanation is similar to ToHexStringUpper
         // constant 55 -> 87 and -7 -> -39 to compensate for the offset 32 between lowercase and uppercase letters
-        public static string? ToHexStringLower(byte[] data)
+        public static string ToHexStringLower(byte[] data)
         {
             if (data == null)
                 return null;
@@ -160,7 +161,7 @@ internal static void InternalWipe<T>(ref T data)
             return new string(c);
         }
 
-        public static byte[]? FromHexString(string hexString)
+        public static byte[] FromHexString(string hexString)
         {
             if (hexString == null)
                 return null;
@@ -172,14 +173,14 @@ internal static void InternalWipe<T>(ref T data)
             return result;
         }
 
-        public static string? ToBase64String(byte[] data)
+        public static string ToBase64String(byte[] data)
         {
             if (data == null)
                 return null;
             return Convert.ToBase64String(data);
         }
 
-        public static byte[]? FromBase64String(string s)
+        public static byte[] FromBase64String(string s)
         {
             if (s == null)
                 return null;
diff --git a/Bifrost.Security/Ed25519.cs b/Bifrost.Security/Ed25519.cs
index 07a4968..3aa168b 100644
--- a/Bifrost.Security/Ed25519.cs
+++ b/Bifrost.Security/Ed25519.cs
@@ -1,5 +1,6 @@
 #pragma warning disable CS8604
 using Bifrost.Security.Internal.Ed25519Ref10;
+using System;
 
 namespace Bifrost.Security
 {
@@ -144,4 +145,4 @@ public static void KeyExchange(ArraySegment<byte> sharedKey, ArraySegment<byte>
             MontgomeryCurve25519.KeyExchangeOutputHashNaCl(sharedKey.Array, sharedKey.Offset);
         }
     }
-}
\ No newline at end of file
+}
diff --git a/Bifrost.Security/MontgomeryCurve25519.cs b/Bifrost.Security/MontgomeryCurve25519.cs
index 8c80ace..d52d21c 100644
--- a/Bifrost.Security/MontgomeryCurve25519.cs
+++ b/Bifrost.Security/MontgomeryCurve25519.cs
@@ -1,6 +1,7 @@
 using Bifrost.Security.Internal;
 using Bifrost.Security.Internal.Ed25519Ref10;
 using Bifrost.Security.Internal.Salsa;
+using System;
 
 namespace Bifrost.Security
 {
diff --git a/Bifrost.Security/Sha512.cs b/Bifrost.Security/Sha512.cs
index c75b8b2..62afa80 100644
--- a/Bifrost.Security/Sha512.cs
+++ b/Bifrost.Security/Sha512.cs
@@ -1,4 +1,5 @@
 using Bifrost.Security.Internal;
+using System;
 
 namespace Bifrost.Security
 {
diff --git a/Bifrost.Security/XSalsa20Poly1305.cs b/Bifrost.Security/XSalsa20Poly1305.cs
index a967d08..c6141be 100644
--- a/Bifrost.Security/XSalsa20Poly1305.cs
+++ b/Bifrost.Security/XSalsa20Poly1305.cs
@@ -1,6 +1,7 @@
 #pragma warning disable CS8604 // Possible null reference argument.
 using Bifrost.Security.Internal;
 using Bifrost.Security.Internal.Salsa;
+using System;
 
 namespace Bifrost.Security
 {
@@ -44,7 +45,7 @@ public static void Encrypt(ArraySegment<byte> ciphertext, ArraySegment<byte> mes
         /// Decrypts the ciphertext and verifies its authenticity
         /// </summary>
         /// <returns>Plaintext if MAC validation succeeds, null if the data is invalid.</returns>
-        public static byte[]? TryDecrypt(byte[] ciphertext, byte[] key, byte[] nonce)
+        public static byte[] TryDecrypt(byte[] ciphertext, byte[] key, byte[] nonce)
         {
             if (ciphertext == null)
                 throw new ArgumentNullException("ciphertext");